1. Field of the Invention
The present invention relates to an ink jet recording apparatus for discharging ink and recording an image on a recording medium. In particular, the present invention relates to a system for detecting or managing the remaining amount of ink in an ink tank that is detachably mounted in an ink jet recording apparatus.
2. Description of the Related Art
As a recording apparatus (hereinafter also referred to as a printing apparatus) using an ink jet technique, there is a well known “bubble jet (registered trade mark)” type recording apparatus wherein ink is evaporated, using thermal energy generated by a heat generating element (heater) employed as a recording element, and is discharged by the expansive force exerted by bubbles formed in the ink during the evaporation process.
However, when this ink jet recording apparatus continues to perform the ink discharge and conduct a recording process after the ink supply has been exhausted, the heated recording head cannot undergo, the cooling effect produced by evaporation. Further, when the recording head continues to be driven under the condition that the ink supply has been exhausted, either the heat generating element of the recording head will be damaged, so there is a danger that thereafter insufficient thermal energy is produced for the discharge of ink, or the heat generating element is actually broken.
To avoid this defect, a method has been practically employed whereby an electric element (hereinafter referred to as an EEPROM), which enables electric erasure and writing, is provided for an ink tank to manage the remaining amount of ink.
According to this method, as ink is consumed, the remaining amount of ink, or the amount of ink consumed, is constantly written to the EEPROM, so that the amount of ink consumed or the remaining amount of ink in the ink tank can be managed. Specifically, methods are available for predicting, based on image data, the amount of ink to be discharged, for counting the number of dots discharged, in accordance with the image data, and for directly counting the number of times the heat generating element was driven.
When through this management a value representing the remaining amount of ink, for example, has reached zero, only the performance of the recording operation need be inhibited to prevent damage to the recording head due to heat generation.
An invention related to the management of the remaining amount of recording agent is disclosed in Japanese Patent Laid-Open Publication No. H05-181364. In this publication, a configuration is proposed whereby an image forming operation is inhibited when the supply of toner has been exhausted, and subsequently, whether or not the toner has been supplemented can be precisely determined, so that the inhibition imposed on the performance of the image forming operation can be correctly removed. Furthermore, according to another configuration, disclosed in Japanese Patent Laid-Open Publication No. H07-025030, management of the image forming process is based on the number of sheets that can be recorded using the remaining ink, and when the ink supply in a tank is exhausted, the image recording process is halted until the empty tank has been replaced by a new one.
By the above described management of the remaining amount of ink, the printing operation is halted when the supply of ink is exhausted to prevent damage to the recording head.
However, depending on environmental conditions, the amount of ink that is actually discharged may vary slightly. Therefore, to avoid a condition wherein the control remaining amount of ink reaches zero before the remaining amount of ink on which the management process is based reaches zero, it has been considered that the latter amount of ink is so managed to reach zero slightly earlier than the former amount of ink. That is, taking user's convenience into account, it is inappropriate for the recording process to be disabled before the remaining amount of ink on which the management process is based reaches zero. In addition, to prevent damage to the recording head and to prompt a user to exchange ink tanks, it is generally employed such the configuration that the remaining amount of ink on which the management process is based is managed to be always lower than the actual remaining amount of ink, and thus it reaches zero before the ink has been exhausted actually.
With this arrangement, when the remaining amount of ink on which the management process is based reaches zero, the actual remaining amount of ink varies due to the above described factors, and it may be anticipated that the remaining ink remains enough to print of several pages. Further, even when the remaining amount of ink on which the management process is based reaches zero during a recording operation, the recording operation may be continued to avoid wasting the recording sheet that is currently being printed. Therefore, in design, there is desirable such specification that even when the remaining amount of ink on which the management process is based reaches zero, the recording operation is continued, or the recording operation is enabled in accordance with an instruction entered by a user.
As is described above, when the recording operation is enabled while the remaining amount of ink reaches zero, the running cost can be reduced, and user convenience is improved. However, if the recording operation is enabled without a limit being set, the ink will actually be exhausted, and a problem will occur.
It is also anticipated that the ink supply system is altered at a user's own risk so as to enable continuous recording even after the remaining amount of ink on which the management process is based reaches zero. In this case, ink may leak from the ink supply system, or a failure may occur due to an ill effect to the mechanism in the recording apparatus. It is difficult for a manufacture of an apparatus to guarantee the apparatus against any failure caused by an unexpected operation. Thus, when an apparatus is modified by a user to enable a recording operation when the remaining amount of ink on which the management process is based reaches zero, it is preferable that the failure of the apparatus itself be avoided and damage to the recording head be minimized. However, the conventional configuration can not cope with this problem.